Blood test might make Parkinson's diagnosis easier, study says

2/11/2017, 6 a.m.

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(CNN)  A new blood test may be as accurate as a test requiring a painful spinal tap for differentiating Parkinson's disease from similar disorders, according to a study published Wednesday in Neurology, the medical journal of the American Academy of Neurology.

Neurological disorders that mimic the symptoms of Parkinson's disease are called atypical parkinsonism disorders.

Many doctors cannot tell whether a patient has Parkinson's disease or atypical parkinsonism.

"This can be very challenging, especially during the early stages of the diseases and if the responsible doctor is not a neurologist specialized in movement disorders," said Dr. Oskar Hansson, lead author of the new study, a neurologist and an associate professor at Lund University in Sweden.

Non-specialists "do not really know exactly what questions to ask the patient and the special signs to look for," Hansson wrote in an email. Yet patients with atypical disorders "usually have a much worse prognosis, with faster disease progression, (with) more disabling symptoms" than Parkinson's patients, so early identification is crucial.

The correct diagnosis is also key to treatment since "most patients with atypical parkinsonism disorders do not respond well to dopamine-targeting medications" that are usually prescribed for Parkinson's patients, Hansson said.

Validating a new biomarker

Hansson and his colleagues developed a blood test that is, essentially, a variation on an existing test capable of detecting neurofilament light chain protein in spinal fluid. This protein is a component of nerve cells, and when these cells die, it can be detected in both spinal fluid and blood.

Because spinal fluid is not easily obtained by a primary care doctor, this diagnostic test is not very useful, so Hansson developed a blood test and investigated its accuracy in the new study.

When validating a new biomarker for disease, "one should always analyze at least two different (groups of patients and controls) to make sure that the results are reproducible," said Hansson, who added that participants should also include both early- and late-stage patients established at different clinics.

All told, a total of 244 people with Parkinson's and 79 healthy volunteers serving as a comparison group participated in Hansson's study, along with 181 patients with atypical parkinsonism disorders.

Of these, 88 patients had multiple system atrophy, which impairs the body's involuntary functions such as heart rate, blood pressure and digestion.

And 23 patients had corticobasal degeneration, which causes decreased movement on one side of the body, muscle rigidity, tremor and a disconnection between thought and action.

Testing these participants, the researchers found that nerve protein levels ranged higher in people with atypical parkinsonism and lower in patients with Parkinson's disease as well as the healthy volunteers. However, the test cannot distinguish between the different atypical disorders, which doctors must rely on symptoms to diagnose.